1. Field of the Invention
The present invention relates to communication satellites, and in particular, to the provision of a high bandwidth, high channel capacity, fully switched, fully interactive communication network in a single satellite. The inventive system is a high capacity communications satellite, or HCCS.
2. Description of the Related Art
Satellites have been used for communication for years. One common use of satellites involves distributed transmission, like the C and Ku band TeleSat, direct broadcast satellites which have one or two beams. These satellites, which are in geosynchronous orbit (i.e. their orbital speed and altitude are such that they seem to hover over a particular position on the earth's surface,) broadcast a series of simultaneous "programs" in one direction to a large number of individual ground stations. These are not point to point or interactive (2-way) satellites. However, they do have a fairly wide bandwidth (typically 100-500 MHz).
Another use for communications satellites is a so-called point to point gateway type use, in which a receiving beam is pointed at a large sending dish (for example, in Europe) and a corresponding transmitting beam is pointed at a receiving dish in the U.S. (for example, Intelsat). This system also is geosynchronous and wideband (100-500 MHz), but has a limited number of beams (for example, eight beams would be a large number for such a system). Also, these systems cover only limited areas, allow only limited switching, if any, and handle very few communication channels.
Some newer system designs (Iridium, Ellipsat, Calling Communications) involve a large number (66 to 840) of low orbit satellites that pass messages among themselves to create a fully interactive network. These are very complex, expensive systems limited to low bandwidth (.apprxeq.10 KHz or less) and low capacity (50-200 channels in the overall system).
Typical satellite communication systems have been limited by low bandwidth (e.g. 50-500 MHz would handle only 50-500 channels); switching networks, using standard video switching capable of inclusion in a satellite, would handle only 10-100 switched channels. Even the present nationwide telephone system handles only audio, which has a much lower bandwidth (.apprxeq.10 KHz), to switch about one million customers simultaneously. The ground telephone system contains 10,000-20,000 switching buildings, at a cost of over $100 billion.
It would be desirable to provide a satellite system having a large number of channels and high bandwidth, while providing a fully switched, interactive system. While optical-based spatial light modulator (SLM) technology is known, and can be used for transmission through the air, as evidenced for example in copending Appln. No. 08/133,879, filed in the name of the present inventor, the application of SLM technology to provide high capacity satellite communications has not been known, so far as the present inventor is aware.